1. Field of the Invention
The present invention relates to an improved continuous flow chemical reaction apparatus with fluid injectors for the introduction of a reactant to a reaction zone under optimized conditions and/or under conditions which avoid explosive regimes.
2. Description of Related Art
Several publications are referenced in this application. The references describe the state of the art to which this invention pertains, and are hereby incorporated by reference.
An oxidative dehydrogenation, or partial oxidation, process is a one step conversion of light hydrocarbons to olefins and carboxylic acids. The process potentially offers many advantages over cracking and pure dehydrogenation which are extremely capital intensive and energy intensive. The conversion of saturated hydrocarbons into olefins and carboxylic acids over low temperature catalysts was disclosed by Thorstienson et al. in a report published in Journal of Catalysis, vol. 52, pp. 116-132 (1978).
U.S. Pat. No. 4,250,346 discloses a process for oxidative dehydrogenation of ethane to ethylene suggesting different low temperature catalyst systems. European Patent No. EP 0 518 548 A2 discloses a process for making acetic acid which comprises oxidizing ethane with molecular oxygen in a reaction zone at a pressure at least 100 psig while the reactants are in contact with a solid catalyst containing vanadium and phosphorous oxides (VPO system).
The oxidative dehydrogenation reaction, however, raises problems such as: (a) removal of the exothermic heat of reaction, (b) possible associated temperature runaway, (c) control of selectivity to desired product, and (d) limiting the formation of undesired oxygenated by-products and carbon oxides.
Another problem which is associated with oxydehydrogenation processes, as well as oxidation processes, is the limitation on the oxidant to hydrocarbon feed ratios which is. imposed by the explosive mixture formation constraint. The imperative of avoiding compositions which can lead to autoignition, deflagration and detonation compromises the ability of the process to achieve optimality of feed compositions that satisfy the stoichiometric and kinetic requirements of the reaction.
These problems have been addressed in a number of patents. Each tried to overcome one or more of the difficulties mentioned above by proposing a modified reactor system or different reactor arrangement.
U.S. Pat. No. 4,899,003 assigned to Union Carbide relates to multi-staging the reactor system where a feed gas comprising ethane and oxygen is converted over an oxydehydrogenation catalyst to a product gas comprising ethylene, acetic acid, water, ethane and carbon oxides. The product gas from each stage (other than the last stage) is cooled and a portion of the acetic acid and water is separated and oxygen is added before passing the product gas stream to the next reaction stage. Total oxygen content in the feed stream to any of the reactors was maintained below 6 mole percent with respect to the total input gaseous stream in that stage.
U.S. Pat. No. 5,583,240 assigned to SRI relates to a reactor with porous membranes to provide for the continuous addition of one reactant all along the reactor and mixing in the entire volume of the reactor to minimize or eliminate local high concentration gradients and hot spots. The other reactant is flowed through the inside of the permeation tube, which contains mixing elements. Those mixing elements were claimed to increase the yield of desired product by increasing the heat and mass transfer rates.
European Patent No. EP 546 677 A1 relates to a fluidized bed for ethane oxidation to acetic acid. The disclosed process included three key steps: (1) cooling the gaseous effluent from the reaction zone; (2) separating most of the acetic acid in liquid form from the effluent gases, leaving a gaseous stream containing nearly all of the carbon oxide contained in the effluent; (3) purging a small portion of said gaseous stream and recycling most of the gaseous stream as part of the feed to the reaction zone. Purging is intended to prevent build-up of carbon oxides in the reaction zone, while recycling serves to maintain a high proportion of carbon oxides in the reaction zone gases, thus aiding in moderating the temperature elevating effect of the highly exothermic oxidation reaction.
U.S. Pat. No. 5,723,094 relates to a chemical reactor design which provides improved micro-mixing conditions and reduced localized zones of concentration to increase reaction selectivity to desired products. The design includes a capillary tubelet positioned within and along the length of flow tubes positioned in a shell reactor and one or more distributors for distributing a first reactant into the flow tubes and a second reactant into the capillary tubes.
European Patent Publication No. 0 532 325 relates to a method and apparatus for the production of ethylene oxide. European Patent Publication No. 0 383 224 relates to a shell-and-tube reactor and method of using the same.
It would be desirable to provide a continuous flow chemical reaction system which provides optimality of feed compositions along a substantial portion of the reaction zone and satisfies the stoichiometric and kinetics requirements of the reaction while maintaining the reaction mixture within the explosive mixture formation constraint and thus avoid reactant mixtures which can lead to autoignition, deflagration and detonation.
It is an object of the invention to overcome the above-identified deficiencies.
It is another object of the invention to provide an improved continuous flow chemical reaction apparatus.
It is another object of the invention to provide an improved continuous flow chemical reaction system where a controlled amount of at least one fluid reactant is introduced into the reaction zone at more than one location.
It is a further object of the invention to provide an improved continuous flow chemical system for performing a catalytic reaction where at least one fluid reactant is introduced into the reaction zone at more than one location.
It is a still further object of the invention to provide an apparatus in which one or more of the reactants is fed in an optimized distributed fashion to meet safety and performance requirements.
It is yet another object of the invention to provide a reactor which achieves a catalyst bed temperature profile controlled by means of non-uniform reactant(s) distribution so that desired operating temperature range is achieved along the entire length of the reactor tube.
It is a still further object of the invention to provide an improved continuous flow chemical reaction system which provides optimality of reacting mixture compositions along a substantial portion of the reaction zone and satisfies the stoichiometric and kinetics requirements of the reaction.
It is a still further object of the invention to provide a reactor wherein the total overall inventory of the reacting mixture falls within an unsafe/explosive composition region, while at any given point or region within the reactor the compositional mixture is within the domain of safe/non-explosive compositions.
The foregoing and other objects and advantages of the invention will be set forth in or apparent from the following description.
The present invention relates to a process and apparatus for the controlled/optimized addition of reactant(s) in continuous flow chemical reactions, preferably oxidative dehydrogenation, partial oxidation or oxidation reactions. More specifically, the invention deals with the shortcomings of these high potential processes by the controlled addition of a reactant which is achieved by means of a central tube or interior conduit along the length of a tubular reactor. The central tube is provided with injector(s) in a specialized configuration capable of introducing a controlled amount of reactant at the injector site into the reaction zone.
The central tube is provided with an injector capable of performing two functions: (1) pressure drop control and (2) flow control. According to one preferred embodiment, the injectors allow for the introduction of a controlled amount of reactant into the reaction zone without allowing any reactant(s) to flow into the injector or the central tube from the reaction zone.
The injector comprises a combination of pressure and flow control elements and an annular injector nozzle. In a preferred embodiment, fluid from the central tube, which in most cases is oxygen, is caused to flow through a precisely sized venturi nozzle to a section of the central tube which is downstream of the annular injector nozzle. The annular injector nozzle is then fed with reactant through a bottle neck nozzle which is connected to the downstream section of the central tube fed by the venturi nozzle. The annular injector nozzle is perpendicularly and circumferentially positioned around the outside of the interior conduit or central tube.
The present design offers a high degree of controllability over the quantity of reactant injection and the locations of the points of injection by adjusting the distance between the injection points. Therefore, injection can be optimized in such a way that only the sufficient and kinetically required amount of reactant is supplied at each point and this is controlled to respond to the spatial variation of the reaction conditions (i.e., temperature, pressure and reaction mixture composition).
The apparatus is suitable for performing continuous flow chemical reactions such as oxidation, oxidative dehydrogenation and partial oxidation processes involving a reactor design characterized by controlled/optimized addition of a reactant with the objective of: (i) avoiding the explosion regime of the reactant mixture (e.g., hydrocarbon/oxidant mixture); (ii) maximizing the selectivity of the reaction to the desired product; (iii) limiting the reactor temperature gradient and therefore the threat of reaction runaway; and (iv) controlling the operating temperature of the reaction zone so that desirable temperature range is maintained over the entire zone.
According to another embodiment, an intermediate or co-feed may be injected which enhances catalyst performance or suppresses a certain poisoning effect. This provides yet another utility of the present invention.
The benefits achievable by using the present invention include the accurate control of the temperature profile along the catalyst bed by controlling the reaction extent and heat release via the quantitative and positional control of reactant addition.
The invention also enhances the catalyst productivity by introducing reactants in proportions which are not possible in conventional reactors due to the explosion regime limitation, and reaction runaway limitation.
The invention also provides a tool for designing the reaction in such a way that the production of the desired product is optimized.
The invention also allows for the adjustment of the reactant mixture composition at every point inside the reactor, as well as the reactor entrance, so that reactant mixtures within the explosion regimes can be avoided.
Furthermore, the invention improves catalyst performance by the delayed addition of a component which reverts its reduction/oxidation state or a component which remedies a catalyst poisoning situation.